June 21, 2010 -- Tumors of skin appendages, such as cancer of the sweat glands, hair follicle, or sebaceous gland, although rare, appear to be increasing in the U.S., a new study shows.

Cutaneous appendageal carcinomas, or skin appendage cancers, are rare and "frequently present a diagnostic challenge," the study researchers write in the June issue of Archives of Dermatology.

Cancers of the sweat glands and other skin-related structures increased dramatically between 1978 and 2005, the researchers say.

The incidence rate of sweat gland cancers has increased 170% since 1978; the rate of all skin appendage cancers has increased 150%. A total of 1,801 patients were identified for incidence analysis, 2,228 for trend analysis, and 1,984 for survival analysis, according to the study, which obtained data from 16 cancer registries in the Surveillance, Epidemiology and End Results Program for the 1978-2005 period.

Men were more likely than women to develop one of the cancers, with an incidence rate of 5.1 cases per 1 million people annually.

Among the study's findings:

Non-Hispanic whites had higher rates of skin appendage cancers than Hispanics, African-Americans, and Asian-Pacific Islanders. Non-Hispanic whites had an incidence rate per million of 5.7, compared to 3.7 for Hispanics, 3.5 for African-Americans, and 2.5 for Asian-Pacific Islanders.

The most common type was cancer of the sweat glands, or more technically, apocrine-eccrine carcinoma.

Incidence rates increased with age. There was a 100-fold difference between patients 20 to 29 and patients 80 and older.

Five-year survival rates were 99% for localized disease, but only 43% for cancers that had spread to other parts of the body.

The cutaneous appendageal carcinomas overall and sebaceous carcinomas occurred disproportionately on the face, scalp, and neck. Disease was less common upper extremities.

The researchers write that the increased incidence rates may be the result of improved recognition and classification of disease. But factors such as exposure to ultraviolet light and immunosuppression also may play a role, the researchers report. They say UV radiation may be a contributing factor, possibly explaining why rates are lower among people with more skin pigmentation.